Regeneration and colonization abilities of the invasive species Elodea canadensis and Elodea nuttallii under a salt gradient: implications for freshwater invasibility

Salinity plays an important role in macrophyte distribution. The current increase in salinization of native freshwaters could modify their susceptibility to invasion. In this study, we determined the tolerance to salt of two invasive macrophytes: Elodea canadensis and Elodea nuttallii. We analysed their growth, regeneration and colonization abilities and the influence of their phenological stage in their response to salt in a laboratory experiment. Traits of both Elodea species varied according to the season and the salt concentration: they were more affected by salt in autumn than in spring, demonstrating higher salt tolerance in spring than in autumn. The two species were sensitive to different thresholds of salinity, although they were both strongly reduced at 3 g l−1 of salt in autumn. Consequently, salt marshes and brackish waters (salt concentration inferior to 3 g l−1 of salt) are likely to be invaded by both species, but the effect of salt levels superior to 3 g l−1 on plant invasiveness needs to be investigated.